In a cellular network communications system, quality of synchronization between base stations directly affects quality of a wireless communication service. With expansion of coverage of a radio base station and improvement of a network, to improve overall user satisfaction, and optimize indicators such as a call drop rate, a call completion rate, a paging success rate, and crosstalk of the network, synchronization between base stations needs to be considered when a transport and backbone synchronization network is built for a wireless network, so that good synchronization performance is extended to a network endpoint to improve overall running indicators of the network.
In a time division system, synchronization is of great necessity and importance. Strict frame number and frame timing synchronization is required between base stations of the time division system; otherwise, mutual interference is caused, and normal operation of a service is affected. In a frequency division system, strict frame number and frame timing synchronization between base stations is not required for some basic services, but when the frequency division system needs to support enhanced services such as an evolved multimedia broadcast and multicast service (eMBMS) and central scheduling power control (CSPC), strict frame number and frame timing synchronization is also required between base stations.
At present, a main technical solution for implementing strict synchronization between radio base stations is to adopt a Global Positioning System (GPS) time service solution, that is, a GPS time service receiver is installed on each base station to receive a time service from a satellite so that base stations perform clock synchronization. Because time references output by different GPS time service receivers are strictly synchronous, frame timing and frame number synchronization may be easily implemented between base stations. Base station clock synchronization of wireless networks all over the world, such as Code Division Multiple Access (CDMA), Time Division-Synchronous Code Division Multiple Access (TD-SCDMA), Long Term Evolution-Time Division Duplex (LTE-TDD), and Worldwide Interoperability for Microwave Access (WIMAX) of time division duplex, basically uses the GPS as a time service reference for base stations. Although the GPS time service solution may well meet a strict phase synchronization requirement between base stations, material costs of a GPS time service are relatively high, engineering installation is difficult, fault maintenance costs are high, and security and reliability are relatively low. Similarly, when another global navigation satellite system (GNSS) such as a GLONASS, GALILEO, or BEIDOU system is used for a base station time service, same problems also exist.